Flow field-flow fractionation and characterization of ionic and neutral polysaccharides of vegetable and microbial origin

The flow field-flow fractionation (FlFFF) analysis of a variety of neutral as well as ionic polysaccharides from plants and micro-organisms shows the generally broad distribution in molecular size of these polymers. This result is also obtained on a commercial sample of pullulan whose size distribution appears much wider than that of any of five standard fractions of the same polymer. Clear evidence of some physico-chemical properties of the polysaccharides is given by the study of the effect of the carrier ionic strength on salep, oxidized salep and konjac, carboxymethylcellulose and hyaluronic acid. While neutral polysaccharides, regardless of their origin, only slightly change size distribution in the presence of a simple electrolyte in solution, charged polymers, either naturally charged or chemically ionized, consistently exhibit very low retention levels in water which dramatically increase even at low salt concentrations. Exclusion mechanisms, including steric effects, are shown to be responsible for the anticipated retention times in water of these species that assume the expected statistical coil behavior only when electric charges are screened by the added electrolyte, Under these conditions, higher retention levels are obtained because the volume adjacent to the accumulation wall becomes more accessible to the sample during relaxation. On the basis of these findings, the elution behavior of a number of polysaccharide samples in-laboratory obtained from the fungus Aureobasidium pullulans under different incubation conditions is attributed to the presence of species varying in physico-chemical properties and molecular size. (C) 2002 Elsevier Science B.V. All rights reserved.